Jarl is the Scandinavian equivalent of earl or duke (cf. English “earl”).
In Norse mythology, Jarl was the son of Ríg(Heimdallr) and Modir(best blood). The Ríg told Jarl about runes and other magic, as well as the language of birds. Jarl then gathered some men and conquered some lands, then married Erna, with whom he had eleven sons, the ancestors of warriors in Norse society.
Earl is a noble title adopted in England since the conquest of Knud, Danish king. responds to the French title of count; it comes after that of marquis. This title first designated the governors of shires or counties. In the 19th century, it was purely honorary and did not imply any function.